Sitecore Forms long labels truncated

The cause of this is fairly straightforward, but given how painful it is to debug I thought I'd post this for anyone else who comes across it.

If you are using Sitecore Forms, and ever have the need to use a very long label in a list item (eg. a checkbox list) you will notice it gets truncated. You may even note that the length is suspiciously similar to the max length of an item name...

After a lot of digging you'll note that these list item label/value strings are altered and set in Sitecore.ExperienceForms.Mvc.DataSource.DataSourceSettingsManager, specifically in the UpdateStaticItems method where there is a call to ItemUtil.ProposeValidItemName() for both label text and value. This is certainly required for one (if it's being set as the name or display name) however not for both.

Thanks to dependency injection the fix is nice and easy to patch in:

<?xml version="1.0"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/"  xmlns:role="http://www.sitecore.net/xmlconfig/role/">
  <sitecore>
    <services>
      <register serviceType="Sitecore.ExperienceForms.FieldSettings.IFieldSettingsManager`1[[Sitecore.ExperienceForms.Mvc.Models.ListFieldItemCollection, Sitecore.ExperienceForms.Mvc]], Sitecore.ExperienceForms" 
        patch:instead="register[@serviceType='Sitecore.ExperienceForms.FieldSettings.IFieldSettingsManager`1[[Sitecore.ExperienceForms.Mvc.Models.ListFieldItemCollection, Sitecore.ExperienceForms.Mvc]], Sitecore.ExperienceForms']"
        implementationType="MyProject.Feature.Forms.DataSource.DataSourceSettingsManager, MyProject.Feature.Forms" lifetime="Transient" />
    </services>
  </sitecore>
</configuration>